The present invention relates to a lens group positioning method for determining a relative relationship between positions of a plurality of lens groups and an image capturing apparatus.
Generally speaking, in a lens unit to be employed for an image capturing optical system provided in a conventional image capturing apparatus, such as a camera, etc., the optical system is constituted by a plurality of lens groups, so as to perform a zooming operation and a focusing operation by driving each of the plurality of lens groups independently from each other.
The image capturing apparatus, in which each of the plurality of lens groups is driven independently from each other so as to perform the zooming operation and the focusing operation, is so constituted that a reference position of each of the plurality of lens groups is detected, and then, the position of each of the plurality of lens groups is controlled by controlling a number of steps for driving a stepping motor from the corresponding reference position detected.
The abovementioned reference position has been detected in such a manner that a light shading plate, integrally mounted on each of the plurality of lens groups, is inserted or withdrawn into/from a gap formed between a light emitting and receiving parts of a photo-interrupter, so as to detect either a position at which a detected signal changes from a light shading state caused by the insertion of the light shading plate to a light receiving state caused by the withdrawal of the light shading plate, or another position at which the detected signal changes from the light receiving state caused by the withdrawal of the light shading plate to the light shading state caused by the insertion of the light shading plate.
Such the lens unit that employs the photo-interrupter to detect the reference position of each of the plurality of lens groups as abovementioned is well-known in this technical field, and for instance, Tokkai 2007-17846 (Japanese Non-Examined Patent Publication) sets forth an example of the above.
In recent years, associating with the size minimization of the lens unit and the trend for pursuing a high variable power capability, sometimes, it has become impossible to secure a desired performance, unless a gap distance between specific lens groups disposed in the vicinity of the image surface (focal plane) is accurately secured specifically.
To accurately secure the gap distance between the lens groups, there has arisen a problem that an assembling error of the photo-interrupter, which is disposed so as to detect the reference position of each of the plurality of lens groups, namely, an error of the reference position, is directly reflected on the error of the gap distance between the lens groups as it is. However, it has been difficult to solve the abovementioned problem, since it is quite difficult to mount two photo-interrupters onto the lens unit while accurately determining the distance between light emitting and receiving parts of the two photo-interrupters at a predetermined value.